In the manufacture of absorbent articles, it is desirable to employ materials having high void volume, a hydrophilic nature, and wet resiliency, or the ability to maintain void volume when wet and when under load. Traditional fluff pulp and creped tissue offer high void volume and are hydrophilic, but they collapse when wetted, especially if a load is applied. Wet laid materials in general suffer from high density due to the largely two-dimensional, planar arrangement of fibers. Air laid materials can have high bulk, but are limited in their stability and resiliency and still have definite limits in porosity and bulk.
Many nonwoven materials made from long synthetic fibers offer high void volume and wet resiliency, but lack inherent hydrophilicity. The fibers can be treated with surfactants or other additives to increase the hydrophilicity of the structure, but such processes are expensive and do not provide the same level of affinity for water offered by cellulose or other hydrophilic polymers. Open cell plastics or plastic foams, also referred to as expanded or sponge plastics, can offer very high void volume and wet resiliency, but suffer the same problem of lacking inherent hydrophilicity and have high cost. Foams made of hydrophilic materials, such as superabsorbent foams, offer the ability to absorb and retain liquids, but can suffer from poor wet resiliency or high cost. Fiber reinforced foams are known wherein fibers are added to increase the strength of a foam matrix, but such materials are generally hydrophobic and lack the high-bulk, absorbent attributes desired of an absorbent article.
Therefore, there is a need for a fibrous structure that has many desirable attributes of a foam, particularly an open-celled foam, but wherein the structure is primarily composed of hydrophilic fibers with fibers serving at least in part as the struts between the open cells.